HCV Screening - Casting the Net
- Initial screen: HCV antibody (anti-HCV) test.
- Detects exposure; indicates past or current infection.
- Becomes positive 4-10 weeks post-exposure.
- Confirmatory test (if anti-HCV positive): HCV RNA PCR.
- Detects active, ongoing infection (viremia).
- Essential for diagnosing chronic HCV & guiding therapy.
- Universal screening: CDC recommends one-time screening for all adults (≥18 years) and all pregnant women during each pregnancy.
⭐ Many individuals with chronic HCV are asymptomatic; universal screening is crucial for early detection and prevention of long-term complications like cirrhosis and hepatocellular carcinoma.
Serology vs RNA - The Core Tests
A two-step process is standard: screen with serology, then confirm active infection with molecular testing.
| Feature | HCV Antibody (EIA) | HCV RNA (PCR) |
|---|---|---|
| Detects | IgG antibodies to HCV proteins | The virus's genetic material directly |
| Indicates | Exposure to HCV (past or current) | Active/current viral replication |
| Window Period | Positive after 2-6 months | Positive as early as 2 weeks |
| Clinical Role | Initial screening test for HCV | Confirms active infection; used to monitor response to antiviral therapy |
| Key Limitation | Doesn't differentiate active vs. resolved infection | Higher cost; not for initial mass screening |
Diagnostic Algorithm - Interpreting Results
Initial screening begins with the HCV antibody (anti-HCV) test. A positive result prompts further testing to differentiate between active and resolved infection.
- Anti-HCV Positive, HCV RNA Positive:
- Indicates active (current) infection.
- Patient is infectious.
- Anti-HCV Positive, HCV RNA Negative:
- Indicates resolved infection.
- Can also be a false-positive anti-HCV screen.
- Anti-HCV Negative:
- Generally rules out HCV infection.
- ⚠️ Exception: May be negative during the early ~2 month "window period" or in severely immunocompromised patients.
⭐ Unlike Hepatitis B surface antibody (anti-HBs), the presence of anti-HCV antibody does not confer immunity or protection against future infection.
- Screening for HCV begins with the HCV antibody test.
- A positive antibody test is followed by HCV RNA PCR for confirmation.
- HCV RNA indicates active infection (acute or chronic).
- Anti-HCV positive, RNA negative suggests a resolved infection.
- During the window period, HCV RNA is detectable 1-2 weeks after infection, while antibodies take longer.
- Quantitative HCV RNA helps monitor treatment response.
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